1. Statement of the Technical Field
The inventive arrangements relate generally to RF systems, and more particularly to embedded sensors for monitoring the state of dielectric fluid used in such systems.
2. Description of the Related Art
Glass ceramic substrates calcined at 850˜1,000 C are commonly referred to as low-temperature co-fired ceramics (LTCC). This class of materials have a number of advantages that make them especially useful as substrates for RF systems. For example, low temperature 951 co-fire Green Tape™ from Dupont® is Au and Ag compatible, and it has a thermal coefficient of expansion (TCE) and relative strength that are suitable for many applications.
Recent interest in fluid dielectric materials suggest the use of LTCC as a substrate because of its known resistance to chemical attack from a wide range of fluids. The material also has superior properties of wetability and absorption as compared to other types of solid dielectric material. These factors, plus LTCC's proven suitability for manufacturing miniaturized RF circuits, make it a natural choice for use in RF devices incorporating fluid dielectrics.
Still, the use of fluid dielectrics raises new potential problems. For example, fluid dielectrics can suffer degradation from a variety of factors. The degradation can occur due to temperature variations, micro-gravity, phase separation, particulate settling and orientation, ionic migration, dendritic growth, and other intrinsic molecular separation phenomena.
Some of these problems are less likely to occur in dynamic systems. However, even in the case of dynamic systems, fluids can separate due to particle fallout, particle separation, sedimentation, eddy effects and so on. These kinds of fluid degradations will effect the overall electrical characteristics of the fluid dielectric, regardless of whether the fluid is a dielectric suspension, dielectric agglomerate, a dielectrically loaded fluid, or a polymer blend.
The refractive index of a substance is generally defined as the ratio of the velocity of electromagnetic radiation in a vacuum to its velocity in the particular substance. Using laboratory equipment, the refractive index of the substance can be determined based on the extent to which the decrease in velocity causes incident radiation to change direction as it passes from one medium to another. Laboratory measurement equipment can be used to measure this change in direction to qualitatively analyze substances for purity and also permit analysis of simple mixtures containing known components.